Flexible, collapsible containers or bags made of plastic have achieved very significant commercial acceptance in the field of parenteral solution and blood bags. Initially, these items have been made from heat-sealed vinyl plastic sheets, and have been quite satisfactory. However, it has been recognized that significant costs can be saved by the use of other manufacturing procedures such as blow-molding and the like. Also, there has been consideration of the use of less expensive materials other than vinyl plastic in containers, particularly those materials that do not contain a plasticizer. For example, polypropylene has been considered a suitable candidate for use as a container material, when extruded as a thin, flexible sheet.
However, it has proven difficult to manufacture thin-walled plastic bags from polypropylene which are capable of collapsing, yet which are strong enough to stand rough handling without breaking. For example, when many filled, conventional designs of collapsible, blow-molded, polypropylene bags are dropped on the floor, they rupture along their tail seal line, which is the point at which the tubular plastic parison, from which the container is made by blow molding, is sealed together at its end.
Accordingly, there is a need for a stronger, thin-walled, collapsible container or bag for use in dispensing blood, parenteral solutions, or any other desired material, which can be made by a blow-molding process or another automated, cost-saving method, and which can be made from plasticizer-free materials such as polyethylene, polypropylene, or other similar plastic materials.
In accordance with this invention, an improved seal structure for plastic containers is disclosed, which may be used with either oriented or non-oriented plastic containers, and flexible or inflexible containers, resulting in a more reliable scaled end for such containers, especially for blow-molded, collapsible containers made from tubular plastic parisons.